Among measuring methods previously proposed in this context can be mentioned the measurement of the thermotension between draw plate and wire-rod, the measurement of the refractive index of the air (Schlieren-methods), resistance measurement (Pirani-principle), thermoelectrical measurement via slide contacts, etc. One method some times applied in the present context is the pyrometric method, in which the black-body temperature of the wire-rod is determined. However, since, among other things, the wire or wire-rod does not function as a black body, it is often necessary to employ complicated two-beam pyrometers or multi-beam pyrometers. Since the temperatures concerned are low from a pyrometric aspect (room temperature to 150.degree. C.) such equipment becomes expensive. In addition it must operate in a dirty environment, which further increases the difficulties. Consequently, no completely practical temperature gauge which is well suited to production conditions has hitherto been available.
British Patent Specification No. 1,334,178 describes apparatus for determining the temperature of an elongated object in contact-less fashion. The apparatus is of the kind described hereinabove and is able to measure the temperature of a plate, which may be moveable. Arranged on one side of the plate is a nozzle-equipped device, from which gas is directed onto the surface of the plate through a circular array of nozzles, there being centrally arranged a suction nozzle which aspires part of the gas through a tube having a temperature sensor mounted therein. The apparatus is intended for ovens, furnaces and the like. This apparatus is not considered suitable for use in connection with more elongated objects, and not at all in conjunction with wire-drawing processes.